---
title: "AEStreamOptionalParam(_:_:)"
framework: coreservices
role: symbol
role_heading: Function
path: coreservices/1444481-aestreamoptionalparam
---

# AEStreamOptionalParam(_:_:)

Designates a parameter in an Apple event as optional.

## Declaration

```swift
func AEStreamOptionalParam(_ ref: AEStreamRef!, _ key: AEKeyword) -> OSStatus
```

## Parameters

- `ref`: An doc://com.apple.documentation/documentation/coreservices/aestreamref containing the stream data.
- `key`: The AEKeyword associated with any keyword/descriptor pair in an Apple event. See doc://com.apple.documentation/documentation/coreservices/aekeyword.

## Return Value

Return Value A result code. See Result Codes.

## Discussion

Discussion Calls to this routine must be preceded by a call to either AEStreamCreateEvent(_:_:_:_:_:_:_:) or AEStreamOpenEvent(_:).  The descriptor associated with the specified key does not need to exist before you call this routine.

## See Also

### Creating Apple Event Structures Using Streams

- [AEStreamClose(_:_:)](coreservices/1449821-aestreamclose.md)
- [AEStreamCloseDesc(_:)](coreservices/1449272-aestreamclosedesc.md)
- [AEStreamCloseList(_:)](coreservices/1448185-aestreamcloselist.md)
- [AEStreamCloseRecord(_:)](coreservices/1449522-aestreamcloserecord.md)
- [AEStreamCreateEvent(_:_:_:_:_:_:_:)](coreservices/1446562-aestreamcreateevent.md)
- [AEStreamOpen()](coreservices/1447732-aestreamopen.md)
- [AEStreamOpenDesc(_:_:)](coreservices/1446544-aestreamopendesc.md)
- [AEStreamOpenEvent(_:)](coreservices/1445366-aestreamopenevent.md)
- [AEStreamOpenKeyDesc(_:_:_:)](coreservices/1442897-aestreamopenkeydesc.md)
- [AEStreamOpenList(_:)](coreservices/1448594-aestreamopenlist.md)
- [AEStreamOpenRecord(_:_:)](coreservices/1447141-aestreamopenrecord.md)
- [AEStreamSetRecordType(_:_:)](coreservices/1447704-aestreamsetrecordtype.md)
- [AEStreamWriteAEDesc(_:_:)](coreservices/1448487-aestreamwriteaedesc.md)
- [AEStreamWriteData(_:_:_:)](coreservices/1442610-aestreamwritedata.md)
- [AEStreamWriteDesc(_:_:_:_:)](coreservices/1450387-aestreamwritedesc.md)
- [AEStreamWriteKey(_:_:)](coreservices/1448750-aestreamwritekey.md)
- [AEStreamWriteKeyDesc(_:_:_:_:_:)](coreservices/1442568-aestreamwritekeydesc.md)